52 INANITION AND MALNUTRITION 



results. When the egg membrane is left around the segmenting ovum in the 

 Ca-free water, complete separation of the cells is prevented, and upon restora- 

 tion to normal sea- water they may reunite and continue normal development. 

 These results of Herbst have been applied in the theory of calcium deficiency in 

 scurvy of vertebrates. 



We have already noted the pioneer work of J. Loeb ('92) in demonstrating 

 the necessity for potassium, sodium and magnesium salts for the normal growth, 

 development and regeneration of the Coelenterate Tubularia. This work was 

 continued by Loeb ('05, 'n), extending his results in general to Echinodermata 

 {Arbacia), Crustacea (Gammarus) and Vertebrates (Fundulus). With the fer- 

 tilized Arbacia eggs, placed in various mixtures of NaCl, KC1, and MgCU, 

 Loeb found that any one salt permitted segmentation (often abnormal) only 

 up to a maximum of 64 cells (in MgCl 2 ). A mixture of two chlorides (MgCl 2 

 and CaCL) may permit reaching the blastula stage; while three chlorides 

 (NaCl, CaClg and KC1) made it possible to reach the gastrula, or even the plu- 

 teus stage, without skeleton. The addition of NaoCOs gave plutei with normal 

 skeleton. 



While Loeb's results are thus to a certain extent in general agreement with 

 those of Herbst, his interpretation of them is quite different. On account 

 especially of his experiments with Fundulus eggs, Loeb believed that the injuri- 

 ous effect of various salt deficiencies is due, not to the direct need for the 

 deficient salt in the developing organism, but rather to the toxic effect of the 

 other salts remaining in solution. Thus Loeb ('05) concludes: "It seems to me 

 that my experiments necessitate the introduction of a new conception, namely, 

 that of physiologically balanced salt solutions. By this I mean salt solutions 

 which contain such ions and in such proportions as completely to annihilate the 

 poisonous effects which each constituent would have if it were alone in solution." 

 The principle that certain salts may function in neutralizing the toxic action of 

 others has been referred to previously in the chapter on plants. 



As to the mechanism of this protective action, Loeb ('11) states: "These 

 observations on the sea-urchin egg, therefore, suggest the possibility that the 

 combination of the three salts in their definite proportion and concentration has 

 the function of forming a surface film of a definite structure or texture, around 

 the protoplasm of each cell, by which the protoplasm is kept together, protected 

 against and separated from the surrounding media." 



The effects of total inanition upon the larvae of the sea-urchin, Strongylo- 

 centrotus lividus, were carefully studied by Runnstrom ('12, '12a). The rate of 

 involution varies directly with the temperature, but the larvae may survive 

 starvation for 60 or 70 days at i8-iq°C, decreasing to one-half the diameter 

 of the original ovum, or less. Two types of involution occur: (1) the skeleton is 

 less affected and the arms persist, although the alimentary canal shows marked 

 changes; or (2) the skeleton is markedly resorbed and the arms greatly shortened, 

 although the other structures may be less changed. In general the hindgut 

 (rectum) undergoes the most marked reduction. The lining epithelial cells 

 becomes first cylindrical, later shortened and finally detached and migratory. 

 The mesenchyme cells are actively phagocytic and migratory, transporting 



